Don't run dhcpcd command when it isn't running

lib/facter/util/linux.rb

@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module Facter
+  module Util
+    module Linux
+      def self.process_running?(process_name)
+        pidfiles = Dir.glob("{/run,/var/run}/#{process_name}{,*,/}*.pid")
+        pidfiles.each do |pf|
+          next unless File.file?(pf)
+
+          pid = begin
+            Integer(Facter::Util::FileHelper.safe_read(pf, '').strip, 10)
+          rescue StandardError
+            nil
+          end
+          next unless pid&.positive?
+
+          begin
+            # Doesn't actually kill, just detects if the process exists
+            Process.kill(0, pid)
+            return true if proc_comm(pid) == process_name || proc_cmdline(pid)&.match?(%r{(^|\s|/)#{process_name}(\s|$)})
+          rescue Errno::ESRCH
+            # If we can't confirm identity, still treat it as not running to be safe.
+            next
+          rescue Errno::EPERM
+            # Exists but we can't inspect it; assume it's running.
+            return true
+          end
+        end
+
+        # Fallback: Try to find it in /proc
+        return false unless Dir.exist?('/proc')
+
+        Dir.glob('/proc/[0-9]*/comm').any? do |path|
+          Facter::Util::FileHelper.safe_read(path, nil)&.strip == process_name
+        end
+      end
+
+      def self.proc_comm(pid)
+        Facter::Util::FileHelper.safe_read("/proc/#{pid}/comm", nil)&.strip
+      end
+
+      def self.proc_cmdline(pid)
+        raw = Facter::Util::FileHelper.safe_read("/proc/#{pid}/cmdline", nil)
+        raw&.tr("\0", ' ')
+      end
+    end
+  end
+end

lib/facter/util/linux/dhcp.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require 'facter/util/linux'
+
 module Facter
   module Util
     module Linux
@@ -73,11 +75,18 @@ def search_internal_leases(interface_name)
           end
 
           def search_with_dhcpcd_command(interface_name)
-            @log.debug("Attempt to get DHCP for interface #{interface_name}, from dhcpcd command")
+            return if interface_name == 'lo'
 
             @dhcpcd_command ||= Facter::Core::Execution.which('dhcpcd')
             return unless @dhcpcd_command
 
+            unless Facter::Util::Linux.process_running?('dhcpcd')
+              @log.debug('Skipping dhcpcd -U because dhcpcd daemon is not running')
+              return
+            end
+
+            @log.debug("Attempt to get DHCP for interface #{interface_name}, from dhcpcd command")
+
             output = Facter::Core::Execution.execute("#{@dhcpcd_command} -U #{interface_name}", logger: @log)
             dhcp = output.match(/dhcp_server_identifier='(.*)'/)
             dhcp[1] if dhcp

spec/facter/util/linux/dhcp_spec.rb

@@ -68,6 +68,12 @@
         allow(File).to receive(:readable?).with('/var/lib/NetworkManager/').and_return(false)
         allow(File).to receive(:readable?).with('/var/db/').and_return(false)
 
+        allow(Dir).to receive(:glob).with('{/run,/var/run}/dhcpcd{,*,/}*.pid').and_return(['/run/dhcpcd.pid'])
+        allow(File).to receive(:file?).with('/run/dhcpcd.pid').and_return(true)
+        allow(Facter::Util::FileHelper).to receive(:safe_read).with('/run/dhcpcd.pid', '').and_return('1234')
+        allow(Process).to receive(:kill).with(0, 1234).and_return(true)
+        allow(Facter::Util::FileHelper).to receive(:safe_read).with('/proc/1234/comm', nil).and_return('dhcpcd')
+
         allow(Facter::Core::Execution).to receive(:which)
           .with('dhcpcd').and_return('/usr/bin/dhcpcd')
         allow(Facter::Core::Execution).to receive(:execute)
@@ -100,5 +106,27 @@
         expect(dhcp_search.dhcp('ens160', 1, log_spy)).to eq(nil)
       end
     end
+
+    context 'when the dhcpcd command is available, but not running' do
+      before do
+        allow(Facter::Util::FileHelper).to receive(:safe_read).with('/run/systemd/netif/leases/1', nil).and_return(nil)
+        allow(File).to receive(:readable?).with('/var/lib/dhclient/').and_return(false)
+        allow(File).to receive(:readable?).with('/var/lib/dhcp/').and_return(false)
+        allow(File).to receive(:readable?).with('/var/lib/dhcp3/').and_return(false)
+        allow(File).to receive(:readable?).with('/var/lib/NetworkManager/').and_return(false)
+        allow(File).to receive(:readable?).with('/var/db/').and_return(false)
+        allow(Dir).to receive(:glob).with('{/run,/var/run}/dhcpcd{,*,/}*.pid').and_return([])
+        allow(Dir).to receive(:glob).with('/proc/[0-9]*/comm').and_return([])
+
+        allow(Facter::Core::Execution).to receive(:which)
+          .with('dhcpcd').and_return('/usr/bin/dhcpcd')
+
+        dhcp_search.instance_eval { @dhcpcd_command = nil }
+      end
+
+      it 'returns nil' do
+        expect(dhcp_search.dhcp('ens160', 1, log_spy)).to eq(nil)
+      end
+    end
   end
 end